1. Field of the Invention
The present invention relates to a liquid jet type recording head for effecting a recording by jetting liquid to form flying droplets.
2. Description of the Prior Art
Great interest has been shown in the ink jet type recording process (liquid jet type recording process) because of its many advantages; for example very little, negligible noise is produced during recording, recording can be carried out at higher speeds and the process does not require any special procedure for fixing the record to so-called ordinary paper.
One of these liquid jet type recording processes is described in Japanese Laid-open Patent Application No. 51837/1979 and German Laid-open Gazette (DOLS) No. 2843064. This process can be distinguished from other liquid jet type recording processes in that thermal energy is caused to act on liquid for providing motive power to discharge liquid drops.
The above described recording process is characterized in that when it is influenced by the thermal energy, the liquid is abruptly increased in volume and then discharged from orifices on the tip of a recording head to form flying drops due to the increased volume of the liquid, these flying drops being adhered to a recording member.
The liquid jet type recording process disclosed in the above DOLS No. 2843064 has a particular advantage in that it can provide images with high quality and resolution at high speed because it can very effectively be applied to the so-called Drop-On Demand recording process and is easily embodied in a full line type high-density multi-orifice recording head.
A recording head portion of a recording system to which the above process is applied comprises a liquid discharge section including orifices for discharging the liquid and liquid passages, each communicating with a corresponding orifice and having a portion in which thermal energy acts on the liquid to discharge liquid drops, and an electro-thermal converting member for generating the thermal energy.
The electro-thermal converting member comprises a pair of electrodes and a heat generating resistive layer having a heat generating region between these electrodes. In general, the electrodes and heat generating resistive layer are covered by a protective layer and located on an insulating base plate. A typical structure of such a recording head is shown in fragmentary section in FIG. 1.
As shown in FIG. 2, an electro-thermal converting member 101 is of a laminated structure which comprises a substrate 102 made of silicon, glass, ceramic or the like, a lower layer 103 on the substrate 102 and made of SiO.sub.2 or the like, a heat generating resistive layer 104 on the lower layer 103 for generating a thermal energy and which is made of Al or the like, an electrode layer 105 located on the heat generating resistive layer 104 for supplying current flows in accordance with information and which is made of SiO.sub.2 or the like, a first upper layer 106 for protecting the heat generating resistive layer 104 and the electrode layer 105, a second upper layer 107 assisting the first upper layer 106 and being made of polyimide or the like, and a third upper layer 108 of Ta or the like for increasing the mechanical strength of the structure. Although the illustrated structure has three upper layers, it is not limited to this, but may be constituted of one or two upper layers or four or more upper layers to protect the layers other than these upper layers. If the materials of the heat generating resistive layer 104 and electrode layer 105 are sufficient for ink-resistance and mechanical strength, the upper layers are not necessarily required.
As viewed from above with the upper layers being removed, the electro-thermal energy converting member has a plane profile shown in FIG. 1 which comprises a plurality of parallel-arranged converting units on the lower layer 201, each of the converting units including a heat generating portion 202, a turned electrode 203 connected with the heat generating portion 202 at one end, and a straight electrode 204 connected with the other end of the heat generating portion 202.
The heat generating portion 202 and the electrodes 203, 204 are generally formed in accordance with the following process. The lower layer 103 is first formed on the substrate 102. The heat generating resistive layer 104 of HfB.sub.2 or the like is then formed on the lower layer 103 by the use of any suitable means such as vapor deposition, sputtering or the like. The electrode layer 105 of Al or the like is further formed on the heat generating resistive layer 104 in a similar manner. Subsequently, the electrode layer 105 and the thermal resistance layer 104 are partially removed with the so-called photo-etching process utilizing a photo-mask which has such a pattern as shown in FIG. 3. Finally, by the similar photo-etching process utilizing a photo-mask of such a pattern as shown in FIG. 4, the electrode layer 105 is further partially removed to form the desired electrode and heat generating portions at the desired positions.
The role of the heat generating portion 202 is to convert electrical energy into thermal energy so that the resulting heat will cause the liquid within the liquid passage to evaporate through the upper layers 106 and 108. The evaporation of the liquid varies its own volume to provide energy for discharging the recording liquid from the liquid jet type recording head. Therefore, the heat generating portion 202 cannot be reduced in size. In order to improve printed letters in quality, the shade of picture elements may be provided by changing the size of liquid droplets. As the size of the heat generating portion is increased, the range throughout which the size of liquid droplets can be changed is correspondingly widened.
On the other hand, it is also important to improve the quality of recorded images by increasing the recording density to raise the resolving power. For such a purpose, the recording head should be of a high-density full multiple head. However, the conventional recording heads have the heat generating portion of the same width W.sub.1 as the width W.sub.2 of the turned electrode so that the recording head cannot compactly be formed with higher density and without decreasing the size of the heat generating portion.